A conventional loudspecker shown in FIG. 8 comprises a T-shaped disc 1, a magnetic iron disc 2 fixed in the inner edge of the T-shaped disc 1, a circular base 3 having an annular flat portion 31 on which is welded the T-shaped disc 1, a voice coil 4, and a cone-shaped diaphragm 5 as its main components.
The circular base 3 also has four trapezoidal openings 32 equally spaced around, and a terminal plate 33 with two terminals for connecting lead wires for the voice coil 4, which is provided between a gap between the protruding-down post and the central opening of the annular flat portion 31 of the circular base 3. The cone-shaped diaphragm 5 is fixed at the outside of the coil 4 and then a protective ring 6 is placed on the central portion of the cone-shaped diaphragm 5.
When the coil 4 receives an alternate current signal, the polar magnetic field between the coil 4 and the magnetic iron 2 produces corresponding magnetic alteration to directly move the voice coil 4, which then moves the diaphragm 5 to vibrate to compress the air around, and the trapezoidal openings 32 serves as air passages for air pressed by the vibration of the diaphragm, thus performing the function of a loudspeaker.
However, the trapezoidal openings 32 is pre-set inadjustable in the conventional art, impossible to realize the reproduced voice as turly as the original voice.